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Diseases and Organisms

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Overview

The U.S. blood supply is safer than it has ever been. However, any bloodborne pathogen has the potential to be transmitted by blood transfusion. Transfusion-transmitted infections (TTIs) are infections resulting from the introduction of a pathogen into a person through blood transfusion. A wide variety of organisms, including bacteria, viruses, prions, and parasites can be transmitted through blood transfusions. The use of a standard donor screening questionnaire as well as laboratory tests help to reduce the risk of an infectious organism being transmitted by blood transfusion.

Bacterial Contamination of Blood Products

Bacterial contamination of blood products, especially in platelets that are stored at room temperature, is the most common infectious risk of blood transfusion, occurring in approximately 1 of 2000-3000 platelet transfusions. Transfusion–transmitted sepsis, while less common, can cause severe illness and death. Improved donor screening as well as improved methods of collection, handling, and storing of blood products has decreased bacterial contamination in recent years.

Gram–positive bacteria normally found on the skin, such as Staphylococcus epidermidis or Staphylococcus aureus, are the most common bacterial contaminants of blood products. This type of contamination is thought to occur when the bacteria on the skin is passed into the collected blood through the collection needle.

Gram-negative bacteria can cause infections including pneumonia, bloodstream infections, wound or surgical site infections, and meningitis. Examples include Acineobacter, Klebsiella, and Escherichia coli (E. coli). Gram-negative bacteria are resistant to multiple drugs and are increasingly resistant to most available antibiotics. Bacteria, such as Escherichia coli (E. coli), may contaminate the donation when blood is collected from donors who have bacterial infection without symptoms.

Anaplasmosis is a tickborne disease caused by the bacterium Anaplasma phagocytophilum. It is transmitted to humans by tick bites primarily from the black-legged tick and the western black-legged tick. Symptoms of anaplasmosis include fever, headache, chills, and muscle aches.

Parasitic Diseases

Transmission of parasitic infections through blood donation is very rare. To help minimize the risk of transfusion-transmitted illnesses, including parasitic infections, donors are asked questions to assist in determining if they are in good health. To reduce the risk of transmitting specific infections (e.g., malaria), donors are asked about recent travel to areas where some infections are more common. Examples of parasitic diseases that can be transmitted by blood transfusion are listed below.

Babesiosis is caused by microscopic parasites that infect red blood cells and are spread by certain ticks. In the United States, tickborne transmission is most common in particular regions and seasons: it mainly occurs in parts of the Northeast and upper Midwest and usually peaks during the warm months.

Chagas disease is caused by the parasite Trypanosoma cruzi, which is transmitted to animals and people by insects. Trypanosoma cruzi is found only in the Americas, and transmission of the parasite occurs mainly in rural areas of Latin America where poverty is widespread. Since 2007, the blood supply has been screened for Chagas disease in the U.S., making the risk of transfusion-transmitted Trypanosoma cruzi extremely rare.

Leishmaniasis includes two major diseases, cutaneous leishmaniasis and visceral leishmaniasis, caused by more than 20 different leishmanial species. Leishmaniasis is transmitted by the bite of small insects called sand flies. The distribution of leishmaniasis is world-wide.

Malaria is a serious and sometimes fatal disease caused by a parasite that commonly infects a certain type of mosquito which feeds on humans. People who get malaria are typically very sick with high fevers, shaking chills, and flu-like illness. About 1,500 cases of malaria are diagnosed in the United States each year. The vast majority of cases in the United States are in travelers and immigrants returning from countries where malaria transmission occurs, many from sub-Saharan Africa and South Asia.

Viral Diseases

Like bacteria and parasites, viruses that are bloodborne and can be transmitted by blood transfusion. Donors are asked questions about their social behavior and health history to help minimize the risk of transfusion-transmitted viral diseases. In addition, blood donations are screened by routine testing for five viral diseases that are potentially transfusion-transmitted: HBV, HCV, HIV, HTLV, and WNV. Examples of viral diseases that can be transmitted through transfusion are listed below.

Dengue fever (DF) is caused by any one of four related viruses transmitted by the mosquitoes. With more than one-third of the world’s population living in areas at risk for transmission, dengue infection is a leading cause of illness and death in the tropics and subtropics. As many as 100 million people are infected yearly.

Hepatitis A is a contagious liver disease that results from infection with the Hepatitis A virus (HAV). Hepatitis A is spread primarily by the fecal-oral route, but transfusion-transmitted HAV infection has been reported. Hepatitis A can range in severity from a mild illness lasting a few weeks to a severe illness lasting several months, and in rare occasions can cause death.

Hepatitis B is a contagious liver disease caused by the Hepatitis B virus (HBV). 1.2 million Americans are living with chronic Hepatitis B, most are unaware of their infection. Over time, approximately 15%–25% of people with chronic Hepatitis B develop serious liver problems, including liver damage, cirrhosis, liver failure, and liver cancer. Every year, approximately 3,000 people in the United States and more than 600,000 people worldwide die from Hepatitis B-related liver disease. Since 1972, the blood supply has been screened for Hepatitis B in the U.S., making the risk of transfusion-transmitted HBV extremely rare.

Hepatitis C is a contagious liver disease caused by the Hepatitis C virus (HBV). Hepatitis C is the most common chronic bloodborne infection in the United States. 3.2 million Americans are living with chronic Hepatitis C, most are unaware of their infection. Chronic Hepatitis C is a serious disease that can result in long-term health problems, including liver damage, cirrhosis, liver failure, and liver cancer. Approximately 12,000 people die every year from Hepatitis C-related liver disease. Since 1992, the blood supply has been screened for Hepatitis C in the U.S., making the risk of transfusion-transmitted HCV extremely rare.

HIV is the human immunodeficiency virus. It is the virus that can lead to acquired immune deficiency syndrome, or AIDS. CDC estimates that about 56,000 people in the United States contracted HIV in 2006. This risk of transfusion-transmitted HIV is extremely remote due to the rigorous testing of the U.S. blood supply.

West Nile virus (WNV) is a potentially serious illness. Experts believe WNV is established as a seasonal epidemic in North America that flares up in the summer and continues into the fall. Symptoms of the illness is include fever, headache, tiredness, aches, and sometimes rash. Although WNV is most often transmitted by the bite of infected mosquitoes, the virus can also be transmitted through contact with infected animals, their blood, or other tissues.

Prion Diseases

Prion Diseases, or transmissible spongiform encephalopathies (TSEs), are a family of rare, progressive neurodegenerative disorders that affect both humans and animals. The causative agent of TSEs is believed to be a prion. A prion is an abnormal, transmissible agent that is able to induce abnormal folding of normal cellular prion proteins in the brain, leading to brain damage and the characteristics signs and symptoms of the disease. Prion diseases are usually rapidly progressive and always fatal. Like viruses, bacteria, and parasites, prions are bloodborne and may be transmitted by blood transfusion.

Variant Creutzfeldt-Jakob Disease (vCJD) is a rare, rapidly progressing neurological disease that causes dementia and death. In 1996, cases of this variant form of Creutzfeldt-Jakob Disease (vCJD) were first reported in the United Kingdom.

Transmission of vCJD in the United Kingdom has been thought to be related to transfusions received years earlier with non-leukoreduced red blood cells from healthy donors who became ill with vCJD months to less than 4 years after the donations. Recipients of blood components from other donors later diagnosed with vCJD remain under surveillance in the United Kingdom and France. The magnitude of the risk of acquiring vCJD from transfusion is uncertain.